The role of cell cycle redistribution in radiosensitization: Implications regarding the mechanism of fluorodeoxyuridine radiosensitization
- Univ. of Wisconsin Medical School, Madison, WI (United States); and other
Radiosensitization has previously been demonstrated in a human colon cancer cell line (HT-29) following a 2 h exposure to low, clinically relevant concentrations (0.05-0.5 {mu}M) of fluorodeoxyuridine (FdUrd) (15). The sensitizer enhancement ratio value (measured at 10% survival) plateaued at {approx} 1.7 between 16 and 32 h following removal of drug. Parallel studies investigating the effect of FdUrd on the distribution of cells throughout the cell cycle found that the percentage of cells in early S-phase increased to {approx} 70% during the same period that maximal radiosensitization was noted. As a follow-up to these findings, experiments have been designed to investigate the contribution of this early S-phase delay to radiosensitization. Synchronized populations of Ht-29 cells have been obtained with three separate techniques. Two involve the induction of a reversible metaphase arrest J(with high pressure N{sub 2}O or colcemid) followed by a shakeoff of mitotic cells. The third uses a plant amino acid, mimosine, to induce a reversible block at the G{sub 1}/S boundary. Flow cytometry was used to analyze the degree of synchrony based on bromodeoxyuridine (BrdUrd) uptake and propidium iodide (PI) staining. Radiation survival curves were obtained on these synchronized populations to investigate changes in radiosensitivity through the cell cycle. Additionally, levels of thymidylate synthase (TS), the primary target of FdUrd cytotoxicity, were measured in each phase of the cell cycle using the TS 106 monoclonal antibody against human TS. Synchronization with mitotic shakeoff produced relatively pure populations of cells in G{sub 1}; however, the degree of synchrony in early S-phase was limited both by cells remaining in G;{sub 1} and by cells progressing into late S-phase. These techniques failed to reveal increased radiosensitivity in early S-phase at 10% survival. 36 refs., 4 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 96062
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 30, Issue 4; Other Information: PBD: 15 Nov 1994
- Country of Publication:
- United States
- Language:
- English
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